LDL is considered to have the function to supply cholesterol to peripheral cells and to be a direct factor in occurrence of various types of arteriosclerosis such as coronary arteriosclerosis. It is known that LDL level in blood is useful as an indicator of arteriosclerosis. The relationship between VLDL which is rich in triglycerides (TG) and arteriosclerosis has also been noted. Currently, the determination of LDL cholesterol is carried out by the ultracentrifugation method, the electrophoretic method, the conversion method, etc., and that of VLDL cholesterol is carried out by the ultracentrifugation method, the electrophoretic method, etc. In the ultracentrifugation method, which is employed as a basic method, LDL or VLDL is separated by the difference in specific gravity using an ultracentrifuge for separation, and the amount of cholesterol therein is determined Adv. Lipid Res., 6, 1 (1968)!. However, this method is defective in accuracy, simplicity, economic efficiency, etc. In the electrophoretic method, LDL or VLDL is separated by using a cellulose acetate membrane or agarose gel as a support, and the amount of cholesterol therein is enzymatically determined Clinical Test (Rinsho Kensa), 29, 1344 (1985)!. This method is defective in simplicity, economic efficiency, etc. In the conversion method, the amount of LDL cholesterol is calculated according to the following equation Clin. Chem.,18, 499 (1972)!. EQU (Amount of LDL cholesterol)=(Amount of total cholesterol)-(Amount of HDL cholesterol)-(Amount of triglycerides)/5
However, the use of this method is restricted by the serum TG content, the type of hyperlipemia, etc., and so this method is defective in simplicity, accuracy, applicability to the analysis of a large number of samples, etc. As described above, conventional methods for the determination of LDL cholesterol or VLDL cholesterol are not suitable for the analysis of a large number of samples, the rapid analysis, and the analysis with an autoanalyzer which is widely used in the field of clinical testing. Further, in these methods, manual errors are liable to occur, for example, when the amount of the LDL fraction separated is determined using a measuring pipette. However, if a blood serum sample is directly added to a reagent containing cholesterol esterase and cholesterol oxidase without fractionation of LDL or VLDL, the resultant test system is not different from a system for the determination of total cholesterol, and LDL cholesterol or VLDL cholesterol cannot be specifically determined.